RELATED APPLICATIONS
There are no applications related hereto heretofore filed in this or any foreign country.
1. Field of Invention
This invention relates generally to powered erasing machines and more particularly to such a machine that automatically extends an elongate cylindrical erasing element to compensate for wear responsive to rotation of the eraser.
2. Background and Description of Prior Art
Electric erasing machines have been known and used for some period of time and during the course of their history their use has become well established, especially in the drafting and graphic arts fields. Most erasing machines have provided elongate abrading type erasing element formed of rubber or similar material that is carried in a body casement, with one erasing element and projecting from the casement for application to a surface to be erased. The erasing element generally is releasably carried in the tool for adjustable extension to compensate for eraser wear and is mechanically rotated by electric or pneumatic power means that may be carried in or otherwise associated with the body casement. The instant invention provides a new and improved tool of this general class.
By reason of the nature of the erasing process, which causes abrasion on the outer end portion of an erasing element, it is necessary to continuously adjust the positioning of the erasing element relative to the tool that carries and rotates it. In general, the cantilevered portion of an erasing element that projects beyond its support in an erasing tool requires adjustment within a fairly limited range of extension to provide proper erasing action. If the projection of the erasing element is too great, it tends to be too elastic to not allow proper force to be exerted upon a surface being erased to cause the abrasion necessary for the erasing process. If the erasing element projection is too little, the pressure on the erasing surface tends to increase, the cone on the eraser tends to be too blunt and the erasing process becomes inefficient, if in fact possible because of chatter and heat.
The requirement for frequent adjustment of eraser extension from an erasing tool has heretofore been recognized and dealt with by various devices that have become known to aid such adjustment. U.S. Pat. No. 2,917,023 issued to Cohen in 1959 shows an erasing machine with a collet holding an elongate erasing element so that the collet may be moved to release the erasing element for outward motion responsive to a biasing force created by a compression spring. U.S. Pat. No. 3,070,379 issued to Misuraca in 1962 shows an elongate erasing element of non-circular cross-section that is carried in an inertial chuck which prevents lineal motion of the erasing element only during periods of its rotation, so that it may be manually moved relative to the erasing tool during inoperative periods. This type of erasing element adjustment, though beneficial, is not automatic and requires manual intervention by an operator to change position of the erasing element relative to the erasing tool.
The instant device, in contradistinction, provides an erasing tool that automatically, by reason of its operation and without manual intervention of an operator, mechanically feeds an elongate erasing element outwardly from the tool's driving mechanism responsive to rotation of the erasing element by that driving mechanism. This type of eraser element feed may be used in hand-held eraser structures of the type that are presently known and the operation of such eraser tools is the same as that with which users have been habitually familiar. The driving and feeding mechanism of the tool also allows use of traditional erasing elements of circularly cylindrical configuration and traditional size that are readily available in the present day marketplace. My mechanism is particularly well adapted for mechanically positionable powered erasing tools for plotters and the like, such as that disclosed in U.S. Pat. No. 4,991,116 issued Feb. 5, 1991 to the instant inventor.
A further advantage of my eraser feeding system is that it provides a frictional type driving mechanism for rotating the cylindrical eraser element that is of a simple mechanical nature to provide greater reliability, smoother operation and lower cost of manufacture. The driving mechanism provides no chuck or collet as such, but rather constitutes three circular cylinders that are angled to each other and to the axis of an erasing element carried therebetween. The erasing element is not mechanically interconnected with the cylinders, but rather is only frictionally engaged by the cylinders so that slippage may occur between the erasing element and the cylinders to prevent damage to the tool or material being erased by reason of the application of excessive force on the erasing element to create excessive friction between the erasing element and workpiece. The parameters determining the amount of frictional engagement between the driving cylinders and the erasing element may be adjusted to prevent generation of excessive heat in the erasing element caused by the application of excessive frictional force between that element and a workpiece. This type of frictional drive also alleviates the use of gear drives and other complex mechanical interconnections between a motor and the erasing element driving mechanism.
My invention resides not in any one of these features individually, but rather in the synergistic combination of all of its structures that necessarily give rise to the functions flowing therefrom.